Detrimental Effect of Unreacted PbI2 on the Long-Term Stability of Perovskite Solar Cells

Excess/unreacted lead iodide (PbI₂) has been commonly used in perovskite films for the state-of-the-art solar cell applications. However, an understanding of intrinsic degradation mechanisms of perovskite solar cells (PSCs) containing unreacted PbI₂ has been still insufficient and, therefore, needs to be clarified for better operational durability. Here, it is shown that degradation of PSCs is hastened by unreacted PbI₂ crystals under continuous light illumination. Unreacted PbI₂ undergoes photodecomposition under illumination, resulting in the formation of lead and iodine in films. Thus, this photodecomposition of PbI₂ is one of the main reasons for accelerated device degradation. Therefore, this work reveals that carefully controlling the formation of unreacted PbI₂ crystals in perovskite films is very important to improve device operational stability for diverse opto-electronic applications in the future.     

Reaction of europium-doped α-SiAlON phosphors with sodium borosilicate glass matrices

The quantum efficiency of composites containing Europium(II)-doped Ca-α-SiAlON phosphors and sodium borosilicate glasses has been reported to decrease with an increase in the Na₂O concentration in the glass matrix. To understand the reason for the dependence of this degradation on the glass composition, the reaction between the SiAlON powder and the glass matrix was investigated using a variety of techniques. SEM images of the areas around SiAlON powders showed the formation of a new layer between the SiAlON particles and the glass matrix. EDX images showed that the number of silicon and aluminium atoms decreased while that of boron atoms increased in the new layer. Raman spectra of the composites showed the formation of BN bonds. New layers between the SiAlON phosphor and the glasses were formed owing to exchange between silicon or aluminium and boron; this resulted in the degradation of the composites.     

Efficient hydrolytic reaction of an acetate ester with fungal lipase in a liquid-liquid interface bioreactor (L-L IBR) using CaCO₃-coated ballooned microsphere

In a liquid-liquid interface bioreactor using a CaCO?-coated ballooned microsphere, 2-ethylhexyl acetate was efficiently hydrolyzed to 2-ethyl-1-hexanol with Absidia coerulea NBRC 4423 compared with using talc-coated or non-coated ballooned microsphere. It was assumed that CaCO? brought about stabilization of lipase by Ca2? and maintenance of medium pH.     

Beef texture characterization using internationally established texture vocabularies in ISO5492:1992: Differences among four different end-point temperatures in three muscles of Holstein steers

‘Tenderness’ has been an important sensory characteristic for beef, although ‘tenderness’ has not been commonly defined. On the other hand, ISO5492:1992 provides internationally established vocabularies for sensory analysis with simple definition. The aim of this study was texture characterization for three beef muscles cooked to four end-point temperatures using ISO5492:1992 texture terms in Japanese to develop objective sensory evaluation terms for beef texture other than ‘tenderness.’ Longissimus, semitendinosus, and psoas major muscles harvested from three Holstein steers were cooked to 45, 60, 72, and 92 °C end-point temperatures and evaluated by a trained sensory panel. Correspondence analysis indicated that the ‘chewiness’ and ‘hardness’ defined in ISO5492 were distinguished in each muscle. Changes in the ‘chewiness’ and ‘hardness’ qualities during cooking were different from each other. These findings suggest that both ‘chewiness’ and ‘hardness’ as defined in ISO5492:1992 should be evaluated simultaneously to determine the sensory texture of beef.     

Evaluation of soft error rates using nuclear probes in bulk and SOI SRAMs with a technology node of 90 nm

The difference of soft error rates (SERs) in conventional bulk Si and silicon-on-insulator (SOI) static random access memories (SRAMs) with a technology node of 90 nm has been investigated by helium ion probes with energies ranging from 0.8 to 6.0 MeV and a dose of 75 ions/μm². The SERs in the SOI SRAM were also investigated by oxygen ion probes with energies ranging from 9.0 to 18.0 MeV and doses of 0.14–0.76 ions/μm². The soft error in the bulk and SOI SRAMs occurred by helium ion irradiation with energies at and above 1.95 and 2.10 MeV, respectively. The SER in the bulk SRAM saturated with ion energies at and above 2.5 MeV. The SER in the SOI SRAM became the highest by helium ion irradiation at 2.5 MeV and drastically decreased with increasing the ion energies above 2.5 MeV, in which helium ions at this energy range generated the maximum amount of excess charge carriers in a SOI body. The soft errors occurred by helium ions were induced by a floating body effect due to generated excess charge carriers in the channel regions. The soft error occurred by oxygen ion irradiation with energies at and above 10.5 MeV in the SOI SRAM. The SER in the SOI SRAM gradually increased with energies from 10.5 to 13.5 MeV and saturated at 18 MeV, in which the amount of charge carriers induced by oxygen ions in this energy range gradually increased. The computer calculation indicated that the oxygen ions with energies above 13.0 MeV generated more excess charge carriers than the critical charge of the 90 nm node SOI SRAM with the designed over-layer thickness. The soft errors, occurred by oxygen ions with energies at and below 12.5 MeV, were induced by a floating body effect due to the generated excess charge carriers in the channel regions and those with energies at and above 13.0 MeV were induced by both the floating body effect and generated excess carriers. The difference of the threshold energy of the oxygen ions between the experiment and the computer calculation might be due to the difference between the designed and real structures.     

Multistep synthesis of VO2 (M) nanoparticles and their application to thermochromic hybrid films for IR modulation

Vanadium dioxide (VO₂) is widely known as one of the excellent thermochromic materials based on a reversible insulator-to-metal phase transition upon temperature change. In this study, VO₂ (M) powder was initially synthesized through a hydrothermal method and a subsequent post-annealing treatment. Additionally, a particle size of the VO₂ (M) powder was reduced and uniformized by introducing a ball-milling process. The resultant VO₂ (M) nanoparticles (NPs) were dispersed in ethanol with the addition of polyvinylpyrrolidone (PVP). The ethanolic dispersion was then coated on a transparent heater used as a substrate by spin-coating to produce VO₂ (M)/PVP composite films. We have attained an exact temperature control of the films by applying voltages to the heater for the assessment of their thermochromic performance such as the solar and the infrared modulation ability. For example, the film temperature could be raised from room temperature to 85.5°C within 180 s at a low voltage of 11 V, which was enough for inducing the phase transition of the VO₂ (M) NPs showing the infrared modulation ability of 19.3%. The combination of the composite films and the heater was thus proved to be a promising way for realizing transparent thermochromic devices.     

In situ Raman spectroscopy analysis of local structure in dry gel for zeolite beta synthesis

To investigate faster crystallization of zeolite beta by the dry-gel conversion method, the local structure of the dry gel before synthesis was quantitatively evaluated using in situ Raman spectroscopy during the drying process. The dry gel prepared from Si and Al sources, and tetraethylammonium hydroxide solution was crystallized after several hours by the dry-gel conversion method. The conformational change of TEA⁺ cations was observed during the drying process by the deconvolution of the spectrum, and the conformational change was larger than that during the synthesis process. The rate of conformational change was increased with the drying temperature, and the apparent activation energy was estimated to be 68.2 kJ/mol. The generation and transformation of double three-membered silicate rings (D3Rs) and 4-2 type secondary building units (SBUs), which are essential for the crystallization of zeolite beta, were observed during the drying process. The transformation from D3R to 4-2 SBU in the dry gel during drying process could be confirmed quantitatively by the difference of the time variation for the amounts of these silicate building units estimated by in situ observation.     

Gas permeation and thermomechanical properties for macroporous alumina focused on necking size at grain boundaries

The gas permeation and thermomechanical properties of macroporous alumina used as a support substrate for microporous ceramic permselective membranes were investigated. The porosity, pore size, and apparent necking size between grains of macroporous alumina were systematically varied, and the relationships between the porous microstructure and material properties were examined. The grain necking size at alumina grain boundaries was evaluated by microstructural observations. The nitrogen gas permeance of the porous alumina increased with increasing pore size. All the measured thermal and mechanical properties decreased with increasing porosity. The properties of porous alumina samples with extensive grain necking showed higher values even in samples with the largest pore size. The high thermal conductivity of porous alumina with extensive grain necking was due to the low interfacial thermal resistance at grain boundaries. Porous alumina with extensive grain necking had high thermal shock strength due to the higher thermal conductivity. It was demonstrated that a porous structure combining high gas permeability and excellent fracture resistance could be successfully achieved.